1. Field of the Invention
The invention relates to a multimode imaging component for dividing or coupling radiation, comprising a waveguide having an end which is provided with at least one window for transmitting radiation into or out of the waveguide. The invention also relates to a ring laser provided with a multimode imaging component.
2. Discussion of the Related Art
A multimode imaging component is also known as multimode interference component and multimode waveguide. The term "multimode imaging" will hereinafter be abbreviated to MMI.
An MMI component is known, inter alia from German Patent Specification DE 25 06 272. This component is very suitable for use as a radiation divider or coupler in integrated optical systems due to its satisfactory suitability for integration with other components, wide manufacturing tolerances, insensitivity to polarization and radiation wavelength, low radiation losses and versatility.
An application of an MMI component is disclosed in the article "Design and fabrication of integrated InGaAsP ring lasers with MMI outcouplers" by M. J. N. van Stralen et al on pp. 2-24 and 2-25 of the conference report of the ECIO '93 in Neuchatel, Switzerland. The MMI component is used in this application for coupling radiation from a ring laser to two output waveguides. The MMI component has two ends each provided with two windows and is arranged in the ring laser in such a way that the MMI component is part of the laser ring in which the radiation is generated. The radiation of the laser ring is passed to the output waveguides via two windows, one at each end. The ring laser, comprising the laser ring, the MMI component and the waveguide, is integrated on a single substrate.
A drawback of this known construction is that the spectrum of the radiation in the output waveguides does not comprise only the desired laser mode of the ring laser under all circumstances, but also a multitude of other, unwanted spectral components.